Exhaust chamber comprising an envelope defining a gas circulation passage

ABSTRACT

An exhaust chamber includes an external envelope ( 10 ), defining a gas circulation passage and at least one continuous wall ( 16, 20, 22, 24 ) along which at least one cover piece ( 26 A,  26 B,  30, 32, 34 ) is arranged, the or each cover piece ( 26 A,  26 B,  30, 32, 34 ) only extending over a limited region of the continuous wall. The dimensions of the cover piece ( 26 A,  26 B,  30, 32, 34 ) and the connection between the cover piece and the continuous wall are selected such that for at least one excitation frequency in the exhaust chamber between 200 Hz and 4 kHz inclusive the cover piece and the continuous wall vibrate with a phase shift of at least 90°. The above finds application in the field of automobile exhausts.

The present invention relates to an exhaust chamber of the type comprising an external envelope delimiting a gas circulation passage and comprising at least one continuous wall, along which at least one cover piece is arranged, the cover piece or each cover piece only extending over a small, limited region of said continuous wall.

In motor vehicles equipped with a heat engine, the exhaust silencer, or any other exhaust chamber provided in the exhaust line to which the engine is connected, is a significant source of sound rays that produce noise pollution in the environment.

In order to reduce sound emissions, it has been conceived to close the external envelope of the exhaust chamber, over the entire external area of the exhaust chamber, with two superimposed layers, between which a sound-insulating material, such as ceramic fibres or a wire mesh, is inserted.

The use of layered material for forming the envelope of the exhaust pipe causes the weight of said pipe to increase and makes its production relatively complex.

The object of the invention is to propose an exhaust chamber that allows sound emissions to be reduced and has a low mass.

For this purpose, the invention relates to an exhaust chamber of the aforementioned type, characterised in that the dimensions of the cover piece and the connection between the cover piece and the continuous wall are such that, for at least one excitation frequency in the exhaust chamber between 200 Hz and 4 kHz, the cover piece and the continuous wall vibrate with a phase shift greater than 90°.

According to particular embodiments, the exhaust chamber comprises one or more of the following characteristics:

-   -   the total area of the continuous wall that is covered by the         cover piece or each cover piece is between 10% and 50% of the         total area of said continuous wall;     -   the dimensions of the cover piece and the connection between the         cover piece and the continuous wall are such that, for at least         one excitation frequency in the exhaust chamber between 200 Hz         and 4 kHz, the cover piece and the continuous wall vibrate in         phase opposition;     -   the dimensions of the cover piece and the connection between the         cover piece and the continuous wall are such that, for at least         one excitation frequency in the exhaust chamber between 200 Hz         and 4 kHz, the cover piece and the continuous wall vibrate with         a phase shift between 90° and 270° for at least 20% of the         frequencies;     -   said continuous wall is a substantially smooth free wall;     -   a single cover piece is arranged on a continuous wall, and said         limited region, along which said cover piece is arranged,         extends approximately in the centre of the evolute of said         continuous wall;     -   it comprises at least two cover pieces arranged on a continuous         wall, and the barycentre of the cover pieces is located         approximately in the centre of the evolute of said continuous         surface;     -   it comprises a transverse wall arranged inside said envelope and         delimiting therein two adjacent chambers, and said cover piece         is arranged along said transverse wall;     -   said cover piece is arranged along said external envelope;     -   said external envelope comprises at least two half-shells that         are joined along a joint, and said cover piece is joined to the         two half-shells in at least two regions of said joint;     -   said cover piece is welded over at least a part of its periphery         to said wall;     -   said continuous wall has a basin in which said cover piece is         confined;     -   it comprises a damping material inserted between the wall and         the cover piece; and     -   over most of its area, said cover piece is juxtaposed against         said continuous wall.

The invention also relates to the use, in an exhaust chamber, for reducing the sound emissions produced by the exhaust chamber comprising an external envelope delimiting a gas circulation passage, and comprising at least one continuous wall, at least one cover piece arranged along the continuous wall, the cover piece or each cover piece only extending over a small, limited region of said continuous wall, the dimensions of the cover piece and the connection between the cover piece and the continuous wall being such that, for at least one excitation frequency in the exhaust chamber between 200 Hz and 4 kHz, the cover piece and the continuous wall vibrate with a phase shift greater than 90°.

A better understanding of the invention will be facilitated by reading the following description, given solely by way of example and with reference to the drawings, in which:

FIG. 1 is a schematic, perspective view of a first embodiment of an exhaust silencer according to the invention;

FIG. 2 is a graph showing, in a silencer according to the invention, the phase difference between a wall and an arranged cover piece, as a function of the frequency;

FIG. 3 is a schematic view of the experimental measuring installation allowing the graph of FIG. 2 to be obtained;

FIG. 4 is a schematic, perspective view of a second embodiment of a silencer according to the invention;

FIG. 5 is a cross-sectional view of a third embodiment of a silencer according to the invention; and

FIG. 6 is a sectional view of a fourth embodiment of a silencer according to the invention.

The exhaust chamber shown in FIG. 1 is an exhaust silencer that is intended to be arranged in the standard part of an exhaust line. It comprises an external envelope 10 delimiting an exhaust gas circulation passage. It has an exhaust gas inlet tube 12 and an exhaust gas outlet tube 14.

The envelope 12 has a lateral, generally cylindrical wall that is elliptical in section, formed by a collar 16 made of a single metal sheet folded back on itself. The opposing longitudinal edges of the collar 16 are connected to each other by a longitudinal weld 18.

At each end, the collar 16 is closed by a transverse end wall 20, 22, commonly known as an “outer cap”.

The end walls 20 and 22 are crossed by the inlet tubes 12 and outlet tubes 14, respectively.

Moreover, one or more intermediate transverse walls 24 delimiting, along the length of the exhaust chamber, a plurality of adjacent chambers, extend inside the gas circulation passage delimited by the envelope 10. These chambers communicate with one another via suitable apertures or conduits. The transverse walls are generally known as “inner caps”.

In the illustrated embodiment, a single intermediate wall 24 is provided inside the exhaust chamber.

The ranges of the collar 16 defined between the caps form continuous walls of the exhaust chamber. Similarly, the ranges of the caps defined between the periphery of the cap and the passage or each passage provided in the cap, form continuous walls.

The term “continuous wall” refers to any wall formed from a single sheet or panel, without this wall being formed from two elements set side-by-side.

Advantageously, these continuous walls are substantially smooth free walls.

More generally, the term “substantially smooth free wall” refers to any convex range of a wall of the exhaust chamber that does not have any protruding and indented cover profiles produced from material, and that is not joined directly to another element of the exhaust chamber, or resting thereon.

In order to reduce noise pollution caused by the circulation of the exhaust gases through the exhaust chamber and by the vibrations of the engine, which spread along the exhaust line, at least one continuous wall of the exhaust chamber has at least one arranged cover piece, the piece or each piece only being juxtaposed against this wall in a limited region of the wall, the total area of the wall that is covered by the cover piece or each cover piece being between 10 and 50% of the total area of said continuous wall.

Advantageously, the wall is free and substantially smooth. The total area covered by the cover piece or each cover piece is then between 10 and 50% of the total area of the substantially smooth free wall.

The envelope 10 delimiting the gas circulation passage comprises, on the stretch of the lateral surface 16 between the end wall 20 and the intermediate wall 24, for example, two discs 26A, 26B that form cover pieces of this type. The discs 26A, 26B are juxtaposed on the outer surface of the collar 16 delimiting the lateral wall of the exhaust silencer.

Advantageously, the discs 26A, 26B are arranged on the free and smooth stretch that is delimited on the collar 16 between the end wall 20 and the intermediate wall 24, such that the isobarycentre of the discs 26A, 26B is substantially conflated with the isobarycentre of the evolute of the free and smooth stretch delimited on the collar.

The term “evolute” of a left wall refers to the flat surface obtained by bringing the left wall along a plane.

Each disc 26A, 26B has, for example, an elliptical shape. It comprises a sheet metal plate that is formed to cling to the shape of the collar 16. Each disc is welded at its periphery to the envelope of the exhaust chamber. Each disc 26A, 26B is connected to the surface of the envelope by a series of separate welds, for example, distributed over the periphery of the disc.

The total area of the free stretch of the collar 16 that is covered by the discs 26A, 26B is, for example, substantially equal to 30% of the total area of this stretch.

Moreover, cover pieces 30, 32 are also juxtaposed locally against the outer surface of the end walls 20 and 22. These cover pieces are formed by metal discs, the area of which is much smaller than the area of the transverse walls 20, 22. These discs are welded at their periphery against the end walls, approximately in the centre of the main smooth range defined by each end wall.

Similarly, a small cover piece 34 is arranged on a face of the intermediate transverse wall 24. As above, this cover piece comprises a metal disc formed from a metal sheet. It is welded against a surface of the intermediate wall, approximately in the centre of a smooth surface thereof.

According to the invention, the dimensions of each cover piece 26A, 26B, 30, 32, 34 and the connection between the cover piece and the associated continuous wall are such that, for at least one excitation frequency in the exhaust chamber between 200 Hz and 4 kHz, the cover piece and the associated continuous wall vibrate with a phase shift greater than 90°. Preferably, this phase shift is greater than 90° for more than 20% of the excitation frequencies from 200 Hz to 4 kHz.

In particular, the dimensions of the cover piece and the connection conditions thereof are such that, in the frequency range in question, the cover piece and the continuous wall vibrate in phase opposition for at least one excitation frequency.

In order to satisfy the above-mentioned requirements, each cover piece may be welded to the continuous wall at an internal point on its surface, marked by reference numeral 35 for the piece 26A in FIG. 1.

FIG. 2 illustrates the development of the phase difference between the cover piece and the continuous wall to which it is applied at a given point on this surface, as a function of the excitation frequency.

In this figure, the curve R illustrates the phase difference measured at a point between the two points of the continuous wall, in the absence of a cover piece. This curve R provides a reference curve.

The curve C illustrates the phase difference, measured at corresponding points of the exhaust chamber, between the cover piece and the continuous wall on which the cover piece is arranged.

The curves in FIG. 2 were obtained using the experimental installation illustrated in FIG. 3.

This installation comprises an excitation case 38, inside which a set of 16 loudspeakers 37, connected to an electrical excitation source 38 that is suitable for applying a sinusoidal, variable-frequency excitation signal to the loudspeakers 37, is arranged.

The internal walls of the case 36 are covered with a sound-insulating material 39. One of the walls of the case arranged opposite the emission face of the loudspeakers has an aperture 40 for the passage of an excitation sound signal. The sample 41 to be tested is joined to the case 36 opposite the aperture 40. This sample comprises a continuous wall 41A of the silencer, on which a cover piece may or may not be arranged.

The cover piece 41B is put in place if it is found on the face of the sample that is turned away from the 16 loudspeakers.

A mechanical accelerometer 42, which is applied at a given point on the wall, is arranged below the continuous wall 41A, on the side of the loudspeakers 37. The accelerometer is connected to a device for recording and processing the signal 43. A laser vibrometer 44, which is also connected to the device 43, is applied at the corresponding point of the cover piece 41A.

The device 43 is suitable for determining, by combining the signals received from the sensors 42 and 44, the phase difference between the corresponding points of the continuous wall 41A and the cover piece 41B.

It will be noted from FIG. 2 that, in the absence of a cover piece, the two faces of the continuous wall vibrate with a phase shift that is substantially zero and less than 45°, whatever the excitation frequency in a range from 150 Hz to 1.2 kHz.

According to the invention, the dimensions of the cover piece and the mode of connecting it to the continuous wall are such that, for at least one frequency, and even from numerous frequencies, the phase shift between the cover piece and the continuous wall is greater than 90°. In particular, the cover piece and the continuous wall are in phase opposition for a plurality of frequencies.

Advantageously, the phase shift between the cover piece and the continuous wall is between 90° and 270° for at least 20% of the excitation frequencies.

It will be understood that in so far as the cover piece and the continuous wall vibrate with a substantial phase shift, the effects of the vibrations of the continuous wall and of the cover piece tend to cancel one another out, such that the assembly formed by the continuous wall and the cover piece is on the whole immobile, thus reducing offensive sound emissions. Under these conditions, the cover piece damps the vibrations produced by the assembly formed by the continuous wall and the associated cover piece.

The presence of the small cover piece or pieces on the walls of the exhaust chamber allows noise pollution to be limited, without significantly increasing the weight of the exhaust chamber.

FIG. 4 illustrates another variation of an exhaust silencer according to the invention. In this embodiment, the envelope 50 is delimited by two half-shells 52, 54, in the form of basins set side-by-side along their edges. The two half-shells 52, 54 are crimped along a peripheral crimping line 56.

A cover piece 70 is juxtaposed locally on the outer surface of the shell 52, approximately in the middle part thereof. This cover piece is formed by a metal strip arranged transversely to the length of the exhaust chamber. The metal strip is formed to cling to the shape of the half-shell 52, and thus to be applied precisely to the outer surface thereof. Each end of the cover piece 70 is received and crimped in the peripheral joint 56 formed between the half-shells 52 and 54.

It will be understood that in this embodiment, too, the cover piece 70, set alongside the half-shell 52 in its middle part, damps the vibrations of the half-shell. Noise pollution produced during the circulation of the exhaust gases in the exhaust chamber is thus reduced, whilst the weight of the exhaust chamber increases only slightly.

FIGS. 5 and 6 illustrate two variations of cover pieces arranged along a wall of an exhaust chamber. As in FIG. 4, this exhaust chamber comprises two half-shells 52, 54, crimped together. However, said exhaust chamber could also be formed from a longitudinally wound and welded collar.

In the embodiment in FIG. 5, a cover piece 80, formed from a metal plate, is received and confined inside a basin 82 formed in the wall of the exhaust chamber. In the illustrated embodiment, this wall is the main surface, marked by reference numeral 84, of the half-shell 52. The basin 82 opens onto the outer surface of the envelope of the exhaust chamber. It has a flat base 86, against which the cover piece 80 is continuously applied. The base 86 is offset relative to the main surface 84 of the wall, toward the interior of the exhaust chamber.

At its periphery, the basin 84 has edges 88 extending above the contour of the plate 80 forming the cover piece. These edges 88 are formed by deformation of the wall 84. The edges 88 retain and immobilise the plate 80, which is clasped between the edges 88 and the base 86 of the basin.

The cover piece 80 is thus immobilised in all directions relative to the wall 84, by being retained in the basin 82.

In order to produce the half-shell 52, a basin 82 is initially moulded into the wall 84, by plastic deformation thereof using a suitable implement. The plate forming the cover piece 80 is then put in place in the basin 82, resting on the base 86. The edges 88 are then pushed above the contour of the cover piece 80 by plastic deformation of the wall 84 using a suitable implement.

It will also be noted in this embodiment that the presence of the cover piece 80, joined by flush-fitting to the wall 84, damps the vibrations and thus reduces noise pollution.

In the embodiment in FIG. 6, a cover piece 90 is arranged by welding on the outer surface 92 of the half-shell 52. In this embodiment, a damping material 94 is arranged between the surface of the wall 92 and the cover piece 90. This damping material comprises, for example, a wire mesh or a resilient, heat-resistant polymer material.

The cover piece 90 is welded at its periphery to the wall 92, along a continuous weld or a set of separate welds.

In this embodiment, the presence of the damping material 94 arranged between the opposing surfaces of the cover piece 90 and the wall 92 ensures that the cover piece and the wall are held apart from each other outside the periphery of the cover piece 90.

Friction between the cover piece 90 and the wall 92 is therefore eliminated, thus reducing the risks of corrosion and wear in the contact regions of these two pieces.

In this embodiment, too, the cover piece damps the vibrations.

Whatever the embodiment, the cover piece is advantageously formed from a metal sheet or a polymer material, the thickness of which is between 0.4 and 1.2 mm, and preferably substantially equal to 0.6 mm. This thickness is, for example, substantially equal to that of the wall on which the cover piece is arranged.

The total area of the cover piece or pieces depends on the surface and the kind of the wall on which it is arranged. This surface is preferably between 10 and 50% of the total area of the free wall to which it is applied. It is advantageously between 20 and 40% of this total area. Its surface is thus between 2 cm² and 2,500 cm² for a motor vehicle exhaust chamber.

A small cover piece may advantageously be arranged on any wall of any kind of exhaust chamber. In particular, a cover piece of this type may be joined to the surface of a convergent or divergent stretch provided at the end of an exhaust chamber containing a catalytic purification member or a particle filter.

A cover piece may also advantageously be arranged on a continuous wall having a covering rib obtained by deformation of the wall. The cover piece is then arranged straddling the rib, for example. In this case, the cover piece is preferably made of polymers. 

1-16. (canceled)
 17. Exhaust chamber comprising an external envelope delimiting a gas circulation passage and comprising at least one continuous wall, along which at least one cover piece is arranged, the cover piece or each cover piece only extending over a small, limited region of said continuous wall, characterised in that the dimensions of the cover piece and the connection between the cover piece and the continuous wall are such that, for at least one excitation frequency in the exhaust chamber between 200 Hz and 4 kHz, the cover piece and the continuous wall vibrate with a phase shift greater than 90°.
 18. Exhaust chamber according to claim 17, characterised in that the total area of the continuous wall that is covered by the cover piece or each cover piece is between 10% and 50% of the total area of said continuous wall.
 19. Exhaust chamber according to claim 17, characterised in that the dimensions of the cover piece and the connection between the cover piece and the continuous wall are such that, for at least one excitation frequency in the exhaust chamber between 200 Hz and 4 kHz, the cover piece and the continuous wall vibrate in phase opposition.
 20. Exhaust chamber according to claim 17, characterised in that the dimensions of the cover piece and the connection between the cover piece and the continuous wall are such that, for at least one excitation frequency in the exhaust chamber between 200 Hz and 4 kHz, the cover piece and the continuous wall vibrate with a phase shift between 90° and 270° for at least 20% of the frequencies.
 21. Exhaust chamber according to claim 17, characterised in that said continuous wall is a substantially smooth free wall.
 22. Exhaust chamber according to claim 17, characterised in that a single cover piece is arranged on a continuous wall, and in that said limited region, along which said cover piece is arranged, extends approximately in the centre of the evolute of said continuous wall.
 23. Exhaust chamber according to of claim 17, characterised in that it comprises at least two cover pieces arranged on a continuous wall, and in that the barycentre of the cover pieces is located approximately in the centre of the evolute of said continuous surface.
 24. Exhaust chamber according to claim 17, characterised in that it comprises a transverse wall arranged inside said envelope and delimiting therein two adjacent chambers, and in that said cover piece is arranged along said transverse wall.
 25. Exhaust chamber according to claim 17, characterised in that said cover piece is arranged along said external envelope.
 26. Exhaust chamber according to claim 25, characterised in that said external envelope comprises at least two half-shells that are joined along a joint, and in that said cover piece is joined to the two half-shells in at least two regions of said joint.
 27. Exhaust chamber according to claim 17, characterised in that said cover piece is welded over at least a part of its periphery to said wall.
 28. Exhaust chamber according to claim 17, characterised in that said continuous wall has a basin in which said cover piece is confined.
 29. Exhaust chamber according to claim 17, characterised in that it comprises a damping material inserted between the wall and the cover piece.
 30. Exhaust chamber according to claim 17, characterised in that, over most of its area, said cover piece is juxtaposed against said continuous wall.
 31. Use for reducing the sound emissions of an exhaust chamber comprising an external envelope delimiting a gas circulation passage, and comprising at least one continuous wall, at least one cover piece arranged along the continuous wall, the cover piece or each cover piece only extending over a small, limited region of said continuous wall, the dimensions of the cover piece and the connection between the cover piece and the continuous wall being such that, for at least one excitation frequency in the exhaust chamber between 200 Hz and 4 kHz, the cover piece and the continuous wall vibrate with a phase shift greater than 90°.
 32. Use according to claim 31, characterised in that the total area of the continuous wall that is covered by the cover piece or each cover piece is between 10% and 50% of the total area of said continuous wall. 